The invention relates to a method for matching data rates for transmitting data via a radio interface between a base station and a subscriber station, especially via broadband radio interfaces which use a CDMA subscriber separation method and simultaneously provide a number of services per call.
In radio communication systems, messages (for example voice, image information or other data) are transmitted via a radio interface with the aid of electromagnetic waves. The radio interface relates to a connection between a base station and subscriber stations where the subscriber stations can be mobile stations or stationary radio stations. The electromagnetic waves are radiated at carrier frequencies in the frequency band intended for the respective system. For future radio communication systems, for example the UMTS (Universal Mobile Telecommunication System) or other third-generation systems, frequencies are provided in the frequency band of approx. 2 000 MHz.
For the third generation of mobile radios, broadband (B=5 MHz) radio interfaces are provided which use a CDMA (Code Division Multiple Access) subscriber separation method for distinguishing between different transmission channels and can simultaneously provide a number of services per call. The problem is how the data of different services of a call are to be time-division multiplexed, i.e. inserted into a frame. The transmission capacity of the radio interface must be utilized in the best possible way, especially taking into consideration a highly dynamic variance in the data rates of the individual services.
From ETSI STC SMG2 UMTS-L1, Tdoc SMG2 UMTS-L1 221/98 of Aug. 25, 1998, especially pages 15-20, it is known to perform a two-stage data rate matching. First data rate matching is performed after channel coding and is intended to guarantee the service-specific qualities of service since the joint transmission of the data of a number of services makes a common signal/noise ratio mandatory. A second data rate matching after the multiplexing guarantees continuous transmission. The disadvantage of this solution can be seen in the fact that it is not possible to minimize the number of required transmission channels or at least, by spreading, the required transmitting power in the transmission channels. The code efficiency also drops since, in part, an expansion followed by a compression or conversely is performed on the same data. The code efficiency specifies the ratio between the change in the bit error rate (BER) and change in the redundancy of the data, the signal/noise ratio being considered as constant.